The present invention relates generally to an ink cartridge and more particularly to an ink cartridge which is suitable for being mounted on a carriage for carrying an ink jet type recording head.
An ink jet recording apparatus such as an ink jet printer comprises an ink jet type recording head carried on a carriage in which pressure is applied to a pressure generating chamber. This chamber is maintained in fluid communication with a common ink tank on one side of the chamber and a nozzle opening on an other. Ink droplets are discharged from the nozzle opening upon the generation of pressure in the chamber. An ink cartridge comprising either the common ink tank or the common ink tank and a plurality of chambers and nozzle openings may be carried on the carriage for supplying the recording head with ink. This ink cartridge is constructed so that ink droplets are discharged onto a recording medium in response to printing data as the carriage is reciprocally moved.
Since the nozzle opening of the recording head is located at a position lower than the ink level in the ink cartridge, fluid pressure of the ink acts on the nozzle opening. A porous material is generally contained in the ink cartridge so that surface tension caused by the porous material allows the pressure inside the ink cartridge to be slightly lower than that at the nozzle opening in order to prevent ink from oozing out from the nozzle opening.
However, as ink is gradually consumed during printing operations and a smaller amount of ink remains absorbed in the porous material, the surface tension caused by the porous material becomes larger and makes it difficult to supply ink to the recording head. Thus, all ink contained in the cartridge will not be completely consumed.
Also, because of the porous material contained in the ink cartridge, the amount of ink stored in the ink cartridge is less than the volume of the ink cartridge by the actual total volume of the porous material. To compensate for the decreased amount of ink in a cartridge employing porous material, a larger ink cartridge is required than would be if the porous material were not employed in order to hold the same amount of ink.
To solve the problem mentioned above, an ink cartridge for an ink jet recording head, for example, as shown in U.S. Pat. No. 4,677,447 (based upon JP-A-62-23 1759), has been proposed. This patent shows an ink tank that is separated into two chambers by a wall formed with a through hole in a lower portion thereof. Ink is provided to the recording head from the first chamber. An umbrella check valve is movably arranged in the through hole. When the ink pressure on the ink head is decreased by expulsion of ink from the chamber, the umbrella check valve is opened to discharge the ink from the into to the cavity, and it is then supplied to the recording head from the first chamber into the second chamber, and it is then supplied to the recording head from the second chamber cavity.
According to the above-mentioned ink cartridge, a porous material need not be contained in the cartridge, so that a larger amount of ink can be substantially stored in the ink cartridge. However, use of the umbrella check valve raises another problem, since its offset amount is too large to finely adjust the amount of ink to be supplied to the recording head. Thus, fluctuations in the amount of ink supplied are caused and the printing quality is degraded.
In addition, since the ink in the first chamber is completely blocked from the recording head when the umbrella check valve is closed, if some change in environmental factors or temperature causes the volume of ink in the second chamber to increase as little as two to five percent, the pressure in the first chamber could increase and break the seal on a connection port which couples the ink cartridge to the recording head. The ink could then leak from the broken seal. Further, when the cartridge is mounted on the recording head, this increased pressure acts on the recording head whereby negative pressure cannot be maintained between the recording head and the ink tank, and thus ink could leak from the recording head.
Furthermore, the umbrella check valve is maintained in a closed state with a pressure difference of approximately 50 mmAq in order to ensure a stable supply of ink to the recording head. However, since this valve closing force is small, the umbrella check valve may open in response to a swinging motion of ink in the ink tank due to the movement of the carriage resulting in temporary pressure differences against the valve from the movement. Thus, stable printing may not be provided.
Additionally, if air enters a recording head while ink is being supplied thereto, the pressure for discharging ink droplets may be absorbed by the air bubble occurring within an ink passage of the recording head. Thus, defective printing may arise when the ink cartridge is exhausted. This problem may also arise if an ink cartridge is removed from a recording head if the ink is not depleted.
Accordingly, it is desirable to provide an ink cartridge which is capable of reliably supplying a recording head with ink in response to a minute pressure difference between the recording head and the ink cartridge, while maintaining negative pressure suitable for printing between the recording head and the ink cartridge, without being influenced by any swinging motion of ink contained therein due to the movement of a carriage upon which the recording head is mounted, and is also capable of preventing ink from leaking from an ink supply port of the cartridge leading to the recording head, or leaking from the recording head, due to temperature or other atmospheric changes.
Additionally, it is desirable to provide an ink cartridge which can prevent air from being drawn into the recording head at the time ink in the ink cartridge is exhausted, or if the ink cartridge is removed before all of the ink is depleted.
Generally speaking, in accordance with the invention, an ink container having an ink supply port formed in one of its walls is separated into two portions by a membrane valve seat made of an elastic thin membrane and formed with a through hole in a central portion thereof. The membrane forms an ink chamber in the portion of the ink container not adjacent the ink supply port and an ink supply chamber in the portion of the ink container adjacent the ink supply port. A valve body is arranged at a position opposite the through hole such that the membrane valve seat is urged to abut the valve body by a pressure difference between the ink chamber and the ink supply chamber, thereby selectively sealing the through hole.
The membrane valve seat receives a pressure difference over a wide area thereof to open a passage from the ink chamber to the ink supply chamber in response to the consumption of a small amount of ink from the ink supply chamber. Thus, the ink can be discharged to a recording head without resulting in excessive negative pressure being imparted on the recording head. Also, if the pressure inside the ink supply chamber increases due to a temperature rise, other environmental factors or the like, the membrane valve seat is responsive to this increased pressure in the ink supply chamber and releases an increased portion of ink from the ink supply chamber to the ink chamber, thereby preventing ink from leaking from the recording head. Further, the membrane valve seat is maintained in close contact with the valve body through its own elasticity to reliably prevent the valve member from bouncing or vibrating due to the movement of the carriage. The ink container may be in the form of an ink cartridge removably mounted on the recording head.
Accordingly, it is an object of this invention to provide an improved ink cartridge capable of reliably supplying ink to a recording head.
Another object of the invention is to provide an improved ink cartridge capable of regulating the pressure imparted to the recording head.
A further object of the invention is to provide an improved ink cartridge capable of regulating the pressure imparted to the recording head and keeping ink from leaking even if temperature changes or other environmental changes cause a change in pressure in the cartridge.
Yet another object of the invention is to provide an improved ink cartridge which prevents air from being drawn into the recording head if the ink in the cartridge is exhausted, or if the ink cartridge is removed before all of the ink is exhausted.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specifications and drawings.
Additionally, the invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.